03 Pyrimidine

Synthesis

  • create monophosphate version

  • II: found in cytosol, rate limiting, inhibited by UMP
  • I: in mito, for urea cycle

  • bifunction: catalyzes 2 steps

  • hypersegmented neutrophils
  • letter U: orotic acid in Urine, Ump synthase, Uridine treatment

Thymidine

  • adding methyl group to create thymidine

  • folate to THF, add carbon to dUMP

  • donate 1 carbon

  • humans don't rely on PABA to make folate

  • deficient in B12: all folate trapped in N5 methyl THF

  • deficient in either folate or B12 leads to high homocysteine level
  • MMA: fatty acid conversion